Abstract: A disk drive is disclosed comprising a disk comprising a plurality of servo tracks defined by servo sectors, a head actuated over the disk, and control circuitry comprising a read channel. A plurality of data tracks are defined relative to the servo tracks, wherein each data track comprises a plurality of segments. The read channel is configured into a read mode in order to first read a first segment of a first data track. During the first read, a quality metric is generated at periodic points along the first segment. After the first read, the read channel is configured into a non-read mode for a predetermined interval. After the predetermined interval, the read channel is configured into the read mode in order to second read the first segment of the first data track and generate the quality metric at the periodic points along the first segment.

Abstract: Method and apparatus for monitoring bi-directional currents in a multi-phase brushless DC motor. The current in each separate phase is separately monitored to generate a feedback signal that is used to dynamically adjust the instantaneous levels of the winding currents in accordance with a specified torque required of the motor. Both negative and positive currents in the motor windings are monitored at all times to provide precision control of the feedback signals.